1. Field of the Invention
The present invention relates generally to a printer, such as thermal printer, an ink jet printer and so forth. More specifically, the invention relates to a printer with a paper supply unit by which it is easy to set the paper in the printer.
2. Description of the Background Art
In recent years, there have been proposed a variety of printers, such as thermal printers, wire-dot printers, ink-jet printers and so forth. Some of the printers employ rolled paper as a printing medium. In conventional printers, a top lid of a casing is arranged so that it can be opened for setting or checking the quantity of a roll of paper. When the quantity of the paper remaining on the roll becomes small, the top lid is opened, the roll of the paper is taken out, and a new roll of paper is set therein. Inspection and maintenance of the printing zone and so forth is also carried out with the top lid open. In such printers, articles must not be placed on the printer and the space on and immediately above the printer should be always empty and vacant. Therefore, this type of printer is not preferable from the viewpoint of the effective utilization of space. Furthermore, the printer cannot be inserted into a unit such as a rack having a narrow horizontal space. When a structure is adopted in which the paper is set in the printer from above, in operation panel or the like is usually arranged on the upper side of a casing, and in this case, the printer must be placed at a low position, for example, on a desk, so that the operation panel can be easily seen. In the reason set forth above, the position of the conventional printer has been strictly limited.
Another type of the conventional printer has been disclosed in the Japanese Utility Model First (unexamined) Publication (Jikkai) Showa No. 61-84935. In the printer construction set out in the above-identified reference, a printer head and a platen are mounted on a printer chassis in a fixed relationship to each other. A space for receiving a roll of paper, such as heat-sensitive recording paper (hereafter referred to as "thermal paper") or so forth, is defined beneath the platen. The space for receiving the roll of the paper will be hereafter referred to as "roll space". When setting the roll of paper in the printer, the roll of paper is, at first, set in the roll space. Thereafter, a manually operable release lever is operated to release the printer head from the platen to form a gap to receive the paper unwinded from the roll. Then, the release lever is again operated to return the printer head toward the platen. By this, the paper is gripped between the printer head and the plane. In this structure, the paper setting operation has been troublesome work. In addition, such conventional printers arrange the printer head, platen and the roll space in vertical alignment, and the thickness of the printer casing has been necessarily large.
For providing a more compact printer which also facilitates easy set of roll of paper, the U.S. Pat. No. 4,641,980 discloses a printer including a casing having a front face, a printing unit, and a control circuit. The printing unit includes a printing medium attaching portion and a printer head portion attached to the printing medium attaching portion. The printing unit is supported in the casing by a moving mechanism so that the printing unit can be freely drawn out forward from the front face of the casing. The moving mechanism also automatically positions the printer head in an open position with respect to the printing medium attaching portion when the printing unit is drawn out from the casing. In the disclosed construction, a draw-out frame is provided in the moving mechanism for easily replacing the roll of paper when the draw out frame is in a position drawn out through the front face. After setting the roll of paper in the roll space defined in the draw-out frame, the frame is moved back into the printer casing. At the fully drawn-in position of the frame, the printer head is placed in contact with the platen with a predetermined biasing force. This means, as long as the frame is set in the printer casing, the printer head is always kept in contact with the platen. Such arrangement tends to cause damaging of the printer head by exerting vibration during transportation or so forth. As well, maintaining the printer head and the platen in contacting condition, secular change, e.g. wearing, deformation and so forth, occurs on the platen to substantially shorten the life of the platen. In addition, by constantly exerting the biasing force, a biasing device may be subject variation or change in its biasing force thereby varying printing performance. In addition, it is the usual practice in such type of printer to insert a spacer between the printer head and the platen to forcibly release the printer head from the platen during transportation. This requires a user's attention to remove the spacer before use. However, since the spacer is held inside of the casing, the user tends to face a difficulty in finding the spacer and removing the same.
In addition, the conventional printers as disclosed in the aforementioned U.S. Pat. No. 4,641,980 drive the drawn-out frame by means of an electric motor. This requires electric power in replacing the rolled paper. This may cause inconvenience if there is need for replacement of the rolled paper without electric driving power for the motor.